A hydrogen supply system of a fuel cell system comes in a number of different modes, and among them, a DE (dead-end) mode is the mode that achieves the greatest power generation efficiency. However, in the DE mode, hydrogen needs to be provided at a stoichiometric ratio of more than 1, and purge needs to be performed periodically to discharge impurities (e.g. water) in the fuel cell to prevent a decline in power generation performance of the fuel cell stack.
However, when the purge is performed, in addition to discharging the impurities, the unused hydrogen is also discharged at the same time. Therefore, as the demand for high-power fuel cells increases in the future, if hydrogen is still supplied in the DE mode, hydrogen consumption will be significantly increased, and fuel efficiency will be reduced.
Accordingly, to enhance the efficiency of the fuel cell and reduce hydrogen consumption, hydrogen discharged by the fuel cell stack is recycled and mixed with hydrogen from a hydrogen source. Currently, hydrogen recycle is performed by using, for example, a hydrogen circulation pump. However, such equipment is not only expensive but also additionally consumes power of the fuel cell.